Myself and colleague are playing Elgars 'In the South' which calls for a rather exposed Aflat to Bflat trill. The only fingering we can come up with is moving right-hand middle finger up and down while fingering the Aflat, but this isnt a very good sounding trill. Does anyone have any suggestions?
Thanks

Try fingering the Bb, using the RH thumb key for the Bb, then trilling with the RH G key.

So it would be: LH XXX Whisper; RH thumb Bb, xx X/O trill

Look at this page, its about halfway down. By the way its a great website for other fingering, alternate or trill